In St_sls_Maker :

chargeSharingOverStrip : calls method ConvertToStrip (StSsdBarrel)-->ConvertToStrip(StSsdWafer) :

- ConvertHitToStrip : take the energy from the GEANT point (GeV) and share it over strips

At this point mStrip->getAnalogSig() is in GeV (DeltaE)

We see a peak at ~0.0001 GeV = 100 keV.

The energy loss of MIP through 300 mu of Si is ~116 kEV, it is consistant with.

- ConvertAnalogToDigit : loop over previous entries and convert the GeV to a number of electrons.

As we know that E_gap = 3.6 eV to create a electron/hole pair, the number of electrons is given by N = DeltaE / e_gap

At this point, mStrip->getDigitSig() is in number of electrons

 the same but in number of electrons : here the maximum is at 20000 electrons.

It is again consistant

The next maker of the simulation chain (St_spa_Maker) simulates the DAQ behavior. It takes a pedestal file and get the pedestal and noise values of strips.

These number are in ADC count.

So a conversion ADC to electron is done.

method readNoiseFromTable : loop over the pedestal file and converts the noise and pedestal according to :

(value_in_ADC) = (value_in_electron) * (1024/(20*22500))

The range of our ADC is 10 bits (2^10 adc channels); it is supposed to cover the full dynamic range of the a128 chip (up to 20 MIP's)

Then knowing 1 MIP = 22500 electrons, we reach the previous relation.

03/31 :

I ran over 50 events to make the plots clearer (in log scale)

Signal of strips in GeV:

(FIGURE 1)

Signal of strips in number of electrons :

(FIGURE 2)

Signal of strips in ADC :

(FIGURE 3)

and finally the charge of clusters :

(FIGURE 4)

So it seems that the peak seen for the charge of clusters (as well as the one for the signal of strips at 614 ADC) is

also here when the charge of the GEANT (FIG. 1and 2) hit is shared over strips.

I looked at the energy loss of the GEANT hit  and I plot :

g2t[i].de

So there is also a peak at 1 MeV. It seems to have an upper limit in GEANT for the loss energy of tracks in SSD.

Tracks with or w/o a SSD hit :

in black are the energy of all SSD hits in GeV in 1 event (for .fz file) and in red are the same energy but for hits where tracks have a SSD hit (in the trackTable, trackTable.n_ssd_hit>0)

Origin of the peak at E =1 MeV : here